This is a continuation-in-part of U.S. patent application Ser. No. 773,376, filed Sept. 9, 1985, now abandoned.
The present invention relates to a fluid friction coupling or clutch unit having interengaging sets of plates which are coupled to a housing substantially filled with a viscous liquid. More particularly, this invention relates to such a fluid friction coupling wherein the plates are separated from one another and are axially displaceable so as to vary the gap between them.
In fluid friction clutches having interengaging sets of plates wherein one set of plates drives the other set of plates, torque is transmitted by the shearing stresses which arise in a viscous fluid disposed in the gaps between the set of plates. The speed of rotation of the driven set of plates and the slippage which occurs within the fluid friction clutch unit, can be regulated by varying the gap width between the plate members, the transferable torque being inversely proportional to the gap width.
In a fluid friction clutch of this type which is described in U.S. Pat. No. 1,238,447, the two sets of elements forming the coupling members are constructed as discs having a plurality of coaxial ring dogs or lugs, the ring lugs being double-conical, i.e., formed with conical inner and outer peripheral surfaces, so that each of the two sets of elements appears comb-like in radial cross-section. The ring lugs of the two discs are directed towards each other and radially offset in alignment with gaps, so that the ring lugs of the one disc can engage into the ring gap of the other discs when an axial displacement of the coupling members represented by the ring lugs takes place. Since these ring lugs have conical inner and outer surfaces, a different gap width results between the interengaging coupling members depending on the depth of penetration of the ring lugs. Thus, the magnitude of torque transferred can be regulated by varying the degree to which the ring lugs penetrate each other.
The fluid friction clutch of U.S. Pat. No. 1,238,447 is of comparatively complicated design, and is expensive to produce, because the discs forming the interengaging elements of the coupling members having the ring lugs must be made with high tolerances. Thus, they cannot be made easily and simply from sheet metal and the like, but require accurate finishing. In addition, fluid friction coupling units of this type must be relatively large in order that the effective surfaces of the coupling members be large enough to transmit relatively high torques. Finally, the design of this fluid friction coupling, in which the gaps are varied by pushing the ring lugs forward or drawing them backwards is an inefficient and complicated design.
A shiftable friction clutch of a different sort is disclosed in European Patent No. 11,908. In this friction clutch, the coupled members are formed as mutually interleaved inner and outer plates which are connected to inner and outer portions of a housing. The inner and outer plates of the friction clutch are axially displaceable by means of a pressure body which can be hydraulically activated. However, the friction clutch of this patent differs from that described hereinabove in many respects. For example, the friction clutch of this patent does not include a viscous fluid. Thus, torque is transferred by pure frictional engagement between the inner and outer plates rather than by the shearing stresses arising in a fluid disposed between the plates. Furthermore, the pressure body disclosed in this patent serves only for engaging and disengaging the plates, rather than to vary the torque which is transmitted between the plates.
British Patent No. 1,412,583 discloses a fluid friction coupling having mutually interleaved inner and outer plates in which torque is transferred by means of a viscous fluid disposed in the gaps between the plates. The fluid friction coupling unit of this patent includes spacers disposed in the gaps between the plates. However, the fluid friction coupling unit of this patent differs from that disclosed herein in failing to provide any means by which the gap width can be actively and dynamically adjusted. Thus, the fluid friction coupling unit of this patent does not contain any biasing elements between the plates which act to spread the plates apart, nor a pressure body which adjusts the magnitude of the gap between the plates.
Accordingly, it is an object of the present invention to provide a fluid friction coupling unit having mutually interengaging sets of plates, wherein the plates are separated from one another and have a viscous fluid therebetween to couple the plates together in rotation.
It is also an object of the present invention to provide such a fluid friction coupling unit wherein the separation between the plates can be actively varied.
It is yet another object of the present invention to provide such a clutch unit which is relatively small, easy to construct, and inexpensive to produce.